On histocompatibility barriers, Th1 to Th2 immune deviation, and the nature of the allograft responses

Abstract

In the present study, we have sought to determine the basis for the frequent failure of Th1 to Th2 immune deviation to blunt the severity of allograft rejection, as such immune deviation has proven highly effective in the treatment of several T cell-dependent autoimmune states. Our study demonstrates that treating islet allograft recipient mice with anti-IL-12 mAb is highly effective in producing Th1 to Th2 immune deviation in several model systems (i.e., fully MHC, partially MHC, or multiple minor Ag barriers). Nevertheless, anti-IL-12 failed to prolong the engraftment of fully MHC-mismatched islet allografts. However, anti-IL-12-treated recipients carrying MHC-matched but multiple minor Ag-mismatched allografts experienced prolonged engraftment; allograft tolerance was frequently achieved in the DBA/2J (H-2d) to BALB/c (H-2d) strain combination. In another model, in which the host response was dominated by CD4+ T cells responding to donor allopeptides presented upon host APCs in the context of self MHC class II molecules, anti-IL-12 treatment proved to be extremely potent. Thus, Th1 to Th2 immune deviation produces prolonged engraftment as compared with recipients of MHC-mismatched allografts when rejection is dependent upon indirectly presented allogeneic peptides and a reduced mass of responding alloreactive T cells.

FIGURE 1

Intragraft expression of Th1 (IL-2 and IFN-γ) and Th2 (IL-4 and IL-10) gene transcripts in MHC-mismatched islet allografts. The islet allografts were harvested on day 8 posttransplant from untreated or anti-IL-12-treated recipient mice, and the intragraft expression of the cytokine gene transcripts was determined by QRT-PCR. THe results are expressed as picograms of target gene cDNA per picogram of GAPDH cDNA. The representative data that were detected in one of three animals in each group are shown.

FIGURE 2

Intragraft expression of Th1 (IL-2 and IFN-γ) and Th2 (IL-4 and IL-10) gene transcripts in MHC-matched but multiple minor Ag-mismatched islet allografts. The islet allografts were harvested on day 16 posttransplant from untreated or anti-IL-12-treated recipient mice, and the intragraft expression of the cytokine gene transcripts was determined by QRT-PCR. The results are expressed as picograms of target gene cDNA per picogram of GAPDH cDNA. The representative data that were detected in one of three animals in each group are shown.

FIGURE 3

Induction of tolerance in anti-IL-12-treated multiple minor Ag-mismatched recipients. Nephrectomy of the islet graft-bearing kidney on five BALB/c recipients at 120 days posttransplantation led to a sharp rise in blood glucose levels. Nephrectomized BALB/c mice accepted a second DBA/2J islet allograft without any immunosuppression.

FIGURE 4

A, Survival of islet allografts from MHC class II KO C57BL/6 mice in thymectomized and CD8⁺ T cell-depleted BALB/c recipients that were treated with anti-IL-12 mAb. B, Intragraft Th1 (IFN-γ)/ Th2 (IL-4) gene transcript analysis in control Ab- or anti-IL-12-treated recipients.

FIGURE 5

FACS analysis of CD4⁺ and CD8⁺ T cells in the peripheral blood of control mice or thymectomized and CD8-depleted recipient mice at the time of allograft rejection. A, isotype control Ab staining; B, unmodified control BALB/c recipients; C, thymectomized and CD8-depleted BALB/c recipients.